1. Field of the Invention
The present invention relates to resorcinolic derivatives for rubber reinforcement and, more particularly, relates to a low fuming novel resorcinolic compound that can be substituted for resorcinol without adversely affecting the cure and mechanical properties of the cured rubber compound.
2. Brief Description of the Prior Art
Resorcinol and resorcinol-formaldehyde resins have been used in the rubber industry as rubber compounds and adhesives. These resorcinolic compounds and resins are unique materials for rubber compounding since they act as thermosetting or vulcanizing plasticizers. They are very efficient plasticizers for rubber during the processing operations. This allows easier processing, higher loading and excellent extrusions of the rubber compounds.
The thermosetting properties of the resorcinol and resorcinol based resins on curing allow material increases in hardness, abrasion resistance, aging resistance, solvent and oil resistance, and stiffness, and give much improved finishes to the cured rubber stock. This combination of plasticizing and reinforcing action is rare for a single material. In addition these resorcinolic resins may act as antioxidants when used in the natural rubber.
Though resorcinol and resorcinol-based resins provide enhanced mechanical and adhesion properties, fuming associated with these materials is a problem to the tire industries. To solve this problem, tire manufacturers are looking for modified resorcinolic derivatives and resins that do not produce volatiles such as resorcinol at Banbury temperatures. In addition to low volatility, the new resorcinolic compound should have reactivity similar to resorcinol and be non-blooming in the rubber compound.
To overcome the problem of fuming, while maintaining equal reactivity like resorcinol, a monoester derivative of resorcinol, namely resorcinol monobenzoate, was used in the rubber compound. Improved dynamic mechanical properties were observed for the cured rubber. Resorcinol monobenzoate and derivatives of resorcinol similar to monobenzoate used in the rubber compositions is disclosed in U.S. Pat. No. 4,605,696. According to this patent the fuming characteristic of the resorcinolic compounds was assessed from the percent weight loss measured by thermogravimetric analysis (TGA). In addition to resorcinol monobenzoate, other resorcinol derivatives such as resorcinol monorosinate, resorcinol diphenyl ether, resorcinol monomethyl ether, resorcinol monoacetate, resorcinol dimethyl ether, phloroglucinol and its derivatives were also evaluated and disclosed in the above patent.
Besides ester and ether derivatives, keto derivatives of resorcinol, which are capable of reacting with methylene donors such as hexamethylenetetramine and hexamethoxymethylmelamine, can also be employed in the rubber compound to enhance the reinforcement and mechanical properties of the cured rubber stock. One such keto derivative of resorcinol is benzoylresorcinol. This benzoylresorcinol is now commercially available and is an excellent UV stabilizer for various polymers.
None of the prior suggests or discloses the use of benzoylresorcinol as a rubber reinforcing compound and which may be employed in the place of resorcinol.
It is, therefore, a primary object of the present invention to provide keto derivatives of resorcinol, such as benzoylresorcinol, which are low fuming but have the cure and reinforcing characteristics like resorcinol in the rubber compound.